Check the listing for details. Vintage 6" Silicon wafer: SP6641 DC-DC boost regulator by Sipex Semiconductor. Listed at 27.50 USD. This sale is for the Sipex silicon wafer, as shown. These are the first Sipex wafers I've ever seen and they are like new right out of the manufacturers shipping carrier. The SP6641 is an ultra-low quiescent current, high efficiency, DC-DC boost converter designed for single and dual cell alkaline, or Li-ion battery applications found in PDA's, MP3 players, and other handheld portable devices. It 's a nice mix of components and has high current power transistors on one side of the chip. Sipex started in 1992 and made a whole line of unique high performance Analog, Power conversion, and mixed signal IC's. I used many of their products myself over the years. They merged with Exar Corporation in 2007 and their still useful products live on today.